加拉帕戈斯群岛达尔文地雀进化的启示

Evolution of Darwin's Finches on the Galapagos Islands

加拉帕戈斯群岛是太平洋中远离大陆的一个群岛,是世界公认的一个大自然生物进化的"实验室"。达尔文于1835年登上该群岛的所见所闻对其进化理论的形成有很大促进作用。群岛上的14种地雀都是该群岛的特有物种,它们都来自南美大陆的一个祖先物种。达尔文地雀的进化与适应性辐射与其他鸟类和动物有着共通性,因此通过对达尔文地雀进化机制和进化过程的研究可以得到很多有益的启示。加拉帕戈斯群岛和夏威夷群岛真正独一无二的地方不是生活在这些岛上鸟类的进化方式,而是这种进化方式是近期内在特定环境条件下发生的,使我们能够亲眼看到这些鸟类的演变和形态歧化的过程和证据。

The Galapagos islands are volcanic. They have never been connected to the mainland. The fourteen species of Darwin＇ s finches fall into four groups： ground finches, tree finches, a warble finch and the Cocos finch. All fourteen species of Darwin＇s finches differ from each other in body size and/or bill, size and shape. The original colonists of the Galapagos must have arrived by overwater flight from the Central or South American continent. Speciation occurred within each group fairly recently. They were all descended from a singie group of colonist. In fact, Galapagos island differ in the characteristics of their food supplies, therefore adaptation to local food supplies is a sufficient explanation for devergence in Galapagos finches. Inter-specific competition for food played a role in the adaptive radiation. Darwin＇s finches represent an early stage in the diver-sification of a group and hence allow us to identify the causes of the origin of an adaptive radiation. Hawaiian archipelago offers a contrasting example of the more typical condition.